Vacuum activation-induced Ti<Superscript>3+</Superscript> and carbon co-doped TiO<Subscript>2</Subscript> with enhanced solar light photo-catalytic activity

Ti³⁺ and carbon co-doped TiO₂ photocatalysts were prepared hydrothermally to introduce the carbon, and followed by simple vacuum activation to achieve the Ti³⁺ self-doping. The prepared co-doped photocatalysts were characterized by XRD, TEM, UV–Vis absorption spectra, EPR, and XPS. It was found that the co-doped TiO₂ has dispersed nanoparticles and a narrower band-gap compared with the un-doped TiO₂ and single-doped TiO₂. The experimental results displayed that the coke carbon generated on the surface of co-doped TiO₂ acts as a photosensitizer and has the photosensitization effect under solar light irradiation. Except for the carbon sensitization effect, the Ti³⁺ self-doping modification has a synergistic effect which is the reason for the effective photo-degradation of methyl orange under simulated solar light irradiation.     

Modeling the active centers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/SiO<Subscript>2</Subscript> and V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> supported catalysts. DFT theoretical analysis of optical properties

Within the framework of the density functional theory (DFT), the electronic structure of monooxodioxovanadium functional groups in tetrahedral coordination, which model the active centers (ACs) of fine supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂, has been analyzed. The optimal structures of three ACs as possible models of monomeric and polymeric oxovanadium forms on the carriers with low vanadium content were determined. The modified DFT method involving the time dependence of Kohn-Sham equation (TDDFT) was used for the adopted AC models to calculate the energies of the excited states, and optical spectra of the absorption in 25000–60000 cm^?1 region were reconstructed on their base. The spectrum in this region is due to O → V charge transfer. The features of electronic spectra with the charge transfer for V₂O₅/SiO₂ and V₂O₅/TiO₂ catalysts and the vibrational spectra of three AC models corresponding to the monomeric and dimeric oxovanadium forms of the supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂ were defined. The detailed interpretation of normal vibration frequencies is given. The frequencies typical of the monomeric and dimeric oxovanadium forms on the carrier surface were identified.     

Preparation of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by mechanical alloying and annealing for sensitizing C-modified TiO<Subscript>2</Subscript> and acquirement of efficient photocatalyst

ZnFe₂O₄ nanoparticles sensitized by C-modified TiO₂ hybrids (ZnFe₂O₄–TiO₂/C) were successfully prepared by a feasible method. The ZnFe₂O₄ nanoparticles were prepared by mechanical alloying and annealing. The residual organic compounds in the synthetic process of TiO₂ were selected as the carbon source. The as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray fluorescence, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible light diffuse reflectance spectroscopy (UV–Vis) and N₂ adsorption–desorption analysis. The photocatalytic activity of the photocatalysts was measured by degradation of methyl orange under ultraviolet (UV) light and simulated solar irradiation, respectively. The results show that the carbon did not enter the TiO₂ lattice but adhered to the surface of TiO₂. The photocatalytic activity of the as-prepared C-modified TiO₂ (TiO₂/C) improved both under UV and simulated solar light irradiation, but the improvement was not dramatic. Introduction of ZnFe₂O₄ into the TiO₂/C could enhance the absorption spectrum range. The ZnFe₂O₄–TiO₂/C hybrids exhibited a higher photocatalytic activity both than that of the pure TiO₂ and TiO₂/C under either UV or simulated solar light irradiation. The complex synergistic effect plays an important role in improving the photocatalytic performance of ZnFe₂O₄–TiO₂/C composites. The optimum photocatalytic performance was obtained from the ZnFe₂O₄(0.8 wt%)–TiO₂/C sample.     

Enhancement of photocatalytic H<Subscript>2</Subscript> evolution over TiO<Subscript>2</Subscript> nano-sheet films by surface loading NiS nanoparticles

NiS/TiO₂ nano-sheet films (NiS/TiO₂ NSFs) photocatalysts were prepared by loading NiS nanoparticles as noble metal-free cocatalysts on the surface of TiO₂ films through a solvothermal method. The prepared samples were characterized by XRD, SEM, EDS, UV–Vis absorption spectra and XPS analysis. The photocatalytic H₂ evolution and photoluminescence spectroscopy (PL) experiments indicated that the NiS cocatalysts could efficiently promote the separation of photogenerated charge carriers in TiO₂ and consequently enhance the H₂ evolution activity. The hydrogen yield obtained from the optimal sample reached 4.31 μmol cm^–2 at 3.0 h and the corresponding energy efficiency was about 0.26%, which was 21 times higher than that of pure TiO₂ NSF. A possible photocatalytic mechanism of NiS cocatalyst on the improvement of the photocatalytic performance of TiO₂ NSF was also proposed.     

Thermal behaviour and properties of Na<Subscript>2</Subscript>O-TiO<Subscript>2</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study the thermal behaviour of (50-x)Na₂O-xTiO₂-50P₂O₅ and 45Na₂O-yTiO₂-(55-y)P₂O₅ glasses. The addition of TiO₂ to the starting glasses (x=0 and y=5 mol% TiO₂) resulted in a nonlinear increase of glass transition temperature and dilatation softening temperature, whereas the thermal expansion coefficient decreased. All prepared glasses crystallize under heating within the temperature range of 300–610°C. The contribution of the surface crystallization mechanism over the internal one increases with increasing TiO₂ content. With increasing TiO₂ content the temperature of maximum nucleation rate is also gradually shifted from a value close to the glass transition temperature towards the crystallization temperature. X-ray diffraction measurements showed that the major compounds formed by glass crystallization were NaPO₃, TiP₂O₇ and NaTi₂(PO₄)₃. The chemical durability of the glasses without titanium oxide is very poor, but with the replacement of Na₂O or P₂O₅ by TiO₂, it increases sharply.     

Entrapment of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in TiO<Subscript>2</Subscript> nanotubes for visible light-driven photocatalysis

In this study, we prepared nanoparticles of the visible light-responsive photocatalyst, Bi₂O₃ entrapped in anatase TiO₂ nanotubes (Bi₂O₃-in-TNTs) via a vacuum-assisted precursor-filling process followed by annealing. Owing to the unique tubular electronic structure of TiO₂ nanotubes, the interior of the nanotube is in an electron-deficient state, which was confirmed by XPS spectra and H₂-TPR. Electrochemical impedance studies showed that the Bi₂O₃-in-TNTs demonstrated a more efficient separation of photogenerated carriers than when Bi₂O₃ nanoparticles were deposited on the outer wall of TiO₂ nanotubes (Bi₂O₃-out-TNTs). Due to the confinement effect of TiO₂ nanotubes, which inhibits photogenerated carriers’ recombination, the Bi₂O₃-in-TNTs exhibited a better photocatalytic performance for the photo-degradation of methyl orange under visible light compared to Bi₂O₃-out-TNTs.     

Synthesis,Adsorptive, and Photocatalytic Properties of Carbon Nanotubes/TiO<Subscript>2</Subscript> Nanocomposite Photocatalysts

The carbon nanotubes/TiO₂ (CNTs/TiO₂) composite photocatalysts composed of TiO₂ nanoparticles and multiwalled carbon nanotubes (CNTs) were prepared by a facile hydrothermal method. The photocatalysts were characterized by a range of analytical techniques including X-ray powder diffraction, field emission scanning electron microscope, thermal gravimetric analysis and UV–Vis optical absorption spectra, etc. The amount of TiO₂ nanoparticles growing on CNTs could be tuned by adjusting the dosage of precursor in the reaction solution. Both the adsorptivity and photocatalytic activities of pure CNTs, pure TiO₂, and the CNTs/TiO₂ nanocomposites were tested by the removal of methylene blue from water in dark and under a simulated sunlight, respectively. By comparison, the improved photocatalytic activity of the CNTs/TiO₂ nanocomposite is mainly due to that the CNTs can disperse the active component of TiO₂ nanoparticles, provide a larger the specific surface area, as well as act as an electron sink to accelerate the separation of the photogenerated charges.     

Phase formation in the V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> system

The solid-phase interaction in the V₂O₅-Nb₂O₅-MoO₃ system has been investigated, and the formation of a solid solution bounded by the compositions MoNb₂V₄O_{18 ? δ}, Mo₂NbV₅O_{21 ? δ}, Mo₂Nb₃V₃O_{21 ? δ}, and Mo₄Nb₉V₉O_{57 ? δ} has been found (δ is nonstoichiometry). In the V₂O₅?Nb₂O₅ system, the formation of three compounds is verified, namely, VNbO₅ (tetragonal structure), VNb₉O₂₅, and V₂Nb₂₃O_62.5. The first two compounds are isostructural and form a continuous solid solution with tetragonal symmetry. A new compound of the composition Mo₃NbVO_{14 ? δ} has been synthesized. This compound is isostructural to the Mo₃Nb₂O₁₄ compound described in the literature and forms a tetragonal solid solution with it. The phase equilibria in the V₂O₅-Nb₂O₅-MoO₃ system in the subsolidus region have been determined.     

Specific heat on Sr<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and Sr<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>7</Subscript>

Summary Specific heats on the single crystals of Sr₂Nb₂O₇, Sr₂Ta₂O₇ and (Sr_1-xBa_x)₂Nb₂O₇ were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T_INC (=495 K) on Sr₂Nb₂O₇ and at the super-lattice phase transition of T_SL (=443 K) on Sr₂Ta₂O₇; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T_LOW (=95 K) on Sr₂Nb₂O₇. The transition temperature T_LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.     

Coal Combustion Synthesis of Coal Cinder-Supported TiO<Subscript>2</Subscript> with Commendable Photocatalytic Activity

Coal cinder-supported TiO₂ photocatalysts were synthesized via a novel coal combustion method. As-obtained samples were characterized by XRD, SEM, EDS mapping, Raman spectra, FTIR and DRS, and their photocatalytic performances were evaluated by degradation of methylene blue (MB) and methyl orange (MO) under UV–Vis light illumination. The results revealed that mixed-phases TiO₂ with adjustable anatase–rutile ratio could be obtained by adjusting the amount of precursor tetrabutyl titanate, which was uniformly covered on the coal cinder. These coal cinder-supported TiO₂ photocatalysts exhibited commendable photocatalytic activity. Among them, the indexed CCT-7.5 sample presented the maximum of activity, which can be attributed to the optimal phase composition of TiO₂. The present work provided a novel synthetic route to fabricate immobilized photocatalysts, which might be extended to the preparation of other functional materials.     

Photocatalytic activity of (sulfur,nitrogen)-codoped mesoporous TiO<Subscript>2</Subscript> thin films

Nitrogen and sulfur co-doped mesoporous TiO₂ thin films were fabricated using thiourea as a doping resource by the combination of the sol–gel and evaporation-induced self-assembly (EISA) processes. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, and UV–vis spectra were performed to characterize the as-synthesized mesoporous TiO₂ materials. The XPS result shows that O–Ti–N and O–Ti–S bonds in the (S, N)-codoped mesoporous TiO₂ were formed. The resultant mesoporous (S, N)-codoped TiO₂ exhibited anatase framework with a high porosity and a narrow pore distribution. After being illuminated for 3 h, methyl orange (MO) could be degraded completely by the co-doped sample under the ultraviolet irradiation, whereas mesoporous TiO₂ film without doping could only degrade 60% MO. After being illuminated by visible light, the water contact angles of the mesoporous co-doped TiO₂ samples decreased slightly, but the pure TiO₂ mesoporous film exhibited no change in the hydrophilicity.     

The effect of PO<Subscript>2,5</Subscript> and AlO<Subscript>1,5</Subscript> additions on structural changes and crystallization behavior of SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> sol-gel derived glasses and thin films

SiO₂-TiO₂-PO_2,5 (STP) and SiO₂-TiO₂-AlO_1,5 (STA) glasses were prepared by sol-gel processing. Their infrared absorption spectra (IR), differential thermal analysis curves (DTA) and X-ray diffraction patterns (XRD) have been recorded. In the SiO₂-TiO₂ system, the chemical homogeneity of the sol-gel glass could be evaluated by the relative concentration of Si-O-Ti heterocondensation comparing to Si-O-Si homocondensation. For the STA system, a gradual decrease of the Si-O-Ti/Si-O-Si band ratio (based on IR spectra) with the addition of Al₂O₃ is observed, with the simultaneous formation of Si-O-Al and Ti-O-Al bounds, i.e Al₃ ⁺ ions are dissolved in the SiO₂-TiO₂ glass matrix and do not promote glass-in-glass phase-separation in the composition range of 0–15 mol% AlO_1.5. In the STP system, on the other hand, P=O bond IR stretch in the ternary glasses indicates that P=O free PO₂O_2/2 ⁻ tetrahedra are formed, rather than the double bonded POO_3/2 tetrahedra that usually occur in binary SiO₂-P₂O₅ glasses. It can be concluded that SiO₂-TiO₂-P₂O₅ glass separates into a SiO₂-rich phase and a TiO₂(P₂O₅)-rich phase. During heat-treatment in STA system only anatase precipitates, even at T ~ 1,000 °C, while in for STP, anatase (TiO₂) or (TiO)₂P₂O₇ (TOP) crystals precipitate at ~600 °C, depending on the P₂O₅ concentration. The major crystal phase, cristobalite, precipitated at ~1,000 °C and at ~1,200 °C, the P-containing phase melts.     

Mechanism and kinetics of formation of La<Subscript>2</Subscript>SrFe<Subscript>2</Subscript>O<Subscript>7</Subscript> and Nb<Subscript>2</Subscript>SrFe<Subscript>2</Subscript>O<Subscript>7</Subscript>

Phase formation processes in the systems Ln₂O₃-SrO-Fe₂O₃ (Ln = La, Nd) in air in the temperature range 1200–1500°C were studied. The synthesis of the complex ferrites La₂SrFe₂O₇ and Nb₂SrFe₂O₇ involves the formation of the intermediate compounds LnFeO₃ and LnSrFeO₄ and occurs by the same mechanism as the synthesis of the corresponding aluminates, but much faster.     

Photomineralization of phenol on Al<Subscript>2</Subscript>O<Subscript>3</Subscript>: synergistic photocatalysis by semiconductors

Phenol gets adsorbed on Al₂O₃ and mineralizes under UV light in the presence of dissolved O₂. The degradation exhibits first-order kinetics and its rate increases linearly with the light intensity and decreases with pH. 2,4-Diphenoxycyclohexanone and 2,6-diphenoxycyclohex-3-ene-1-ol are the intermediates of the reaction. While particulate TiO₂, ZnO, ZnS, Fe₂O₃, CuO, CdO, and Nb₂O₅ individually photocatalyze the degradation, each semiconductor exhibits synergistic photocatalysis, an enhanced photodegradation, when present along with Al₂O₃, indicating electron abstraction by illuminated semiconductors from the phenol adsorbed on Al₂O₃.     

Hierarchically nanostructured porous TiO<Subscript>2</Subscript>(B) with superior photocatalytic CO<Subscript>2</Subscript> reduction activity

Hierarchically nanostructured, porous TiO₂(B) microspheres were synthesized by a microwave-assisted solvothermal method combined with subsequent heat treatment in air. The materials were carefully characterized by scanning and transmission electron microscopy, X-ray diffraction, CO₂ adsorption, and a range of spectroscopies, including Raman, infrared, X-ray photoelectron and UV-Vis spectroscopy. The hierarchical TiO₂(B) particles are constructed by ultrathin nanosheets and possess large specific surface area, which provided many active sites for CO₂ adsorption as well as CO₂ conversion. The TiO₂(B) nanostructures exhibited marked photocatalytic activity for CO₂ reduction to methane and methanol. Anatase TiO₂ and P₂5 were used as the reference photocatalysts. Transient photocurrent measurement also proved the higher photoactivity of TiO₂(B) than that of anatase TiO₂. In-situ infrared spectrum was measured to identify the intermediates and deduce the conversion process of CO₂ under illumination over TiO₂(B) photocatalyst.     

Catalytic Properties of TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles in Plasma Chemical Treatment

We proposed here a new process coupling dielectric barrier discharge (DBD) plasma with magnetic photocatalytic material nanoparticles for improving yield in DBD degradation of methyl orange (MO). TiO₂ doped Fe₃O₄ (TiO₂/Fe₃O₄) was prepared by the sol-gel method and used as a new type of magnetic photocatalyst in DBD system. It was found that the introduction of TiO₂/Fe₃O₄ in DBD system could effectively make use of the energy generated in DBD process and improve hydroxyl radical contributed by the main surface Fenton reaction, photocatalytic reaction and catalytic decomposition of dissolved ozone. Most part of MO (88%) was degraded during 30 min at peak voltage of 13 kV and TiO₂/Fe₃O₄ load of 100 mg/L, with a rate constant of 0.0731 min^?1 and a degradation yield of 7.23 g/(kW h). The coupled system showed higher degradation efficiency for MO removal.     

Enhancement of the photoluminescence and long afterglow properties of Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript> phosphor by Dy<Superscript>3+</Superscript> co-doping

The Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺, Dy³⁺ long afterglow phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by powder X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) techniques. The luminescence properties were investigated using thermoluminescence (TL), photoluminescence (PL), long afterglow, mechanoluminescence (ML), and ML spectra techniques. The crystal structure of sintered phosphors was an akermanite type structure, which belongs to the tetragonal crystallography. TL properties of these phosphors were investigated, and the results were also compared. Under the ultraviolet excitation, the emission spectra of both prepared phosphors were composed of a broad band peaking at 535 nm, belonging to the broad emission band. When the Ca₂MgSi₂O₇:Eu²⁺ phosphor is co-doped with Dy³⁺, the PL, afterglow and ML intensity is strongly enhanced. The decay graph indicates that both the sintered phosphors contain fast decay and slow decay process. The ML intensities of Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphors were proportionally increased with the increase of impact velocity, which suggests that this phosphor can be used as sensors to detect the stress of an object.     

A new phosphor with flower-like structure and luminescent properties of Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> long afterglow materials by sol–gel method

The flower-like phosphors of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ with high brightness and long afterglow were obtained by sol–gel method. X-ray diffraction pattern (XRD) shows that single-phased Sr₂MgSi₂O₇ phosphor is prepared by sol–gel method under 1250 °C. Scanning electron microscope (SEM) indicates that the phosphor consists of nano-sized whiskers which are detected for the first time in Eu²⁺ and Dy³⁺ co-doped long-lasting phosphorescence silicates. Furthermore, the investigation on the mechanism indicates that the internal structure and gas, liquid and solid phase effect play important roles in the formation of flower-like Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ nanostructure. Finally, the optical properties of flower-like Sr₂MgSi₂O₇ nanostructure have been characterized by photoluminescence (PL) spectra.     

Sol–gel synthesis,characterization and photocatalytic activity of mesoporous TiO<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3 </Subscript>granules

Mesoporous TiO₂/γ-Al₂O₃ composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH₃ decomposition, TiO₂/γ-Al₂O₃ granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO₂/γ-Al₂O₃ granules using titania made by hydrothermal method had comparable performance in NH₃ decomposition.     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.